The polymer-analogous functionalization of polymer end groups to give five-membered cyclic carbonate groups is prior art. For instance, DE102007023867 describes the functionalization of the compounds containing amino groups with glycerol carbonate chloroformate. The formation of the amide groups proceeds quantitatively. However, the preparation of the acid chloride from glycerol carbonate constitutes an additional reaction step.
A further synthesis route is the reaction of 4-tosylmethyl-1,3-dioxolan-2-one with hydroxyl-terminated polymers, for example polyethers. Here too, it is not glycerol carbonate but a derivative which is used, the latter being prepared from glycerol carbonate beforehand.
The polymer-analogous reaction with commercially available, unmodified glycerol carbonate is described in EP328150. The free alcohol in the glycerol carbonate is reacted with anhydride groups in a polymer. However, polymers having anhydride groups, because of their high reactivity, are generally not obtainable during the reaction process but only after polymer-analogous reaction. This is especially true of polyamides and polyesters, which are synthesized by means of polycondensation.
The reaction of hydroxyl-terminated polymers with unsubstituted glycerol carbonate has likewise been described. They are joined to one another via diisocyanates, which react with the alcohol groups both of the polymer and of the glycerol carbonate to give the urethane. This can be effected via a reaction stage as described, for example, in JP 06145264 A, in which the polyols are mixed simultaneously with diisocyanate and glycerol carbonate. The disadvantage is that covalent joining of two polymers with a molecule of diisocyanate results in chain extensions.
An alternative, controlled process is a two-stage synthesis route first to give the isocyanate-terminated prepolymer which is then reacted with glycerol carbonate. WO 2006010408 describes this procedure for hydroxyl-terminated polyesters.
A disadvantage of the latter processes is that isocyanates are used. Isocyanates, especially non-polymer-bound isocyanates of low molecular weight, are a matter of toxicological concern. Therefore, complex occupational hygiene measures have to be taken in the course of production, and corresponding labelling of the product is required. In addition, it is necessary to ensure that, in the final use, the release of isocyanates into the breathable air or through migration is prevented.
The particular aim of using the carbonate-functionalized polymers in isocyanate-free polyurethane systems is to avoid isocyanates.
WO 2012007254 describes an isocyanate-free joining operation via a stoichiometric coupling with dicyclohexylcarbodiimide rather than diisocyanates, wherein the base polymers are prepared by ring-opening reaction. The polymerization reaction described can give only OH-terminated polymers which then have to be reacted with an anhydride in order to obtain the acid termination. For instance, the polyol first has to be reacted with succinic anhydride, for example. The resultant carboxyl end groups react in a second reaction step with glycerol carbonate. This is effected in dichloromethane with addition of activating reagents. Overall, this two-stage process is very complex and also cannot be conducted without solvent or catalytically.